Elucidation of the detailed transition state (T. S.) structures of acyl transfer for enzymic and model reactions by structure reactivity correlations and by the Beta-D probe along with its temperature dependence, lately, implicated solvent reorganization as (partially) rate limiting in some of these. It is proposed, that the application of the Beta-D probe to aryl acetate model reactions with unsolvated nucleophiles, solubilized by 18-crown-6 in aprotic solvents would reveal much more about the importance of solvent reorganization in acyl transfer. The Beta-D isotope effects can be calculated from spectrophotometric rate measurements and evaluated in comparison to Beta-D effects on the same reactions in water and methanol. Theoretical calculations of the Beta-D probe on some typical acyl-transfer reactions from aryl acetate in the presence and absence of a small number of water molecules is a more remote objective of this project.